Active Dewatering Of Limestone Quarry And Drinking Water Production – Feasibility Assessment Using A Groundwater Model
Cotton, Alan (1); Orban, Philippe (2); Wildemeersch, Samuel (3); Collon, Pauline (4); Hallet, Vincent (1); Brouyère, Serge (2)
1: University of Namur, Belgium; 2: University of Liège, Belgium; 3: SPAQuE S.A., Belgium; 4: University of Lorraine, France
Belgium has a great abundance of two main natural resources, groundwater and rocks. Owing to its small surface, geological framework and high population density, most of the quarries have to be deepened instead of expanded laterally. In such cases, the bottom of the extraction pit could reach the groundwater table and a dewatering system has to be set up to lower the piezometric head to ensure continuity of production in dry conditions. Most of the time, open-pit quarry dewatering is achieved by installing a sump, which is usually the lowest-cost solution. However, this action affects the regional hydrogeology and, in some cases, the productivity of nearby groundwater catchments for drinking water supply. Moreover, runoff waters collected in the sump are not of sufficiently high quality to be used as such for drinking water production without a heavy treatment. Therefore, the only viable option to reconcile both dewatering and drinking water supply is by means of drilling deep perimeter wells.
This alternative has been the choice of Lhoist Industries Ltd., regarding its project of deepening the Boverie limestone quarry in Rochefort (Belgium). Two Devonian limestone reefs are currently exploited in this quarry for high-grade lime production. The groundwater table contained in these formations is drained by the Tridaine gallery, an artificial gravity-driven groundwater catchment, which will dry up if the deepening project comes true. This gallery provides drinking water for both the city of Rochefort and Saint-Remy’s Abbey of Rochefort, the latter using it as a major raw material in the fabrication process of one of the 14 Trappist beers in the world.
In order to assess the feasibility of the dewatering of the Boverie quarry using a single perimeter well, with a sufficient discharge to lower the piezometric head beneath the quarry while fulfilling the water demand of both the city and abbey, we developed a numerical finite elements groundwater flow model using the SUFT3D code. The results show that the use of a single perimeter well is appropriate to achieve the complete dewatering of the quarry and the drinking water supply. However, the model highlights that the aquifer exploitation has to be managed more dynamically, by varying the discharge rate of the well during high water and low water periods.